kernel: Pass interrupt reference to chainman

This and the following commit seek to decouple the libbitcoinkernel
library from the shutdown code. As a library, it should it should have
its own flexible interrupt infrastructure without relying on node-wide
globals.

The commit takes the first step towards this goal by de-globalising
`ShutdownRequested` calls in kernel code.

Co-authored-by: Russell Yanofsky <russ@yanofsky.org>
Co-authored-by: TheCharlatan <seb.kung@gmail.com>

src/test/blockmanager_tests.cpp

@@ -25,7 +25,7 @@ BOOST_AUTO_TEST_CASE(blockmanager_find_block_pos)
         .chainparams = *params,
         .blocks_dir = m_args.GetBlocksDirPath(),
     };
-    BlockManager blockman{blockman_opts};
+    BlockManager blockman{m_node.kernel->interrupt, blockman_opts};
     CChain chain {};
     // simulate adding a genesis block normally
     BOOST_CHECK_EQUAL(blockman.SaveBlockToDisk(params->GenesisBlock(), 0, chain, nullptr).nPos, BLOCK_SERIALIZATION_HEADER_SIZE);